What I find is that for many lenses (including the Canon 28/2.8) reputations can be all over the map. The 28/2.8 that I bought recently is an early version and it's very soft in the corners wide open. I borrowed a different 28/2.8 when I tested the R-D1 and it was much better. So, I imagine the best thing to do is to keep trying different examples and see (firsthand) how they do.
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